1. Field of the Invention
Without limiting the scope of the invention, the present invention relates generally to embedding digital data in an analog signal, and more particularly, to systems, methods, and devices for spread spectrum data hiding with multiple channels of hidden data for multiple users.
2. Description of the Related Art
During a phone call, a participant may desire to not only transmit voice but to also supplement the voice with data content. An audio system which can transmit additional data has many different uses. For example, such additional data may be related to an ongoing teleconference (referred to herein as conference). For example, the data may be related to an ongoing audio conference or video conference.
The data is digital, while the voice is analog. There are a number of ways to combine digital data and voice signals together. For example, one way is to use digital telephone channels such as an internet link or ISDN-based channels. The digital data can be multiplexed with digitized voice. This method is limited, however, to channels that are digital end-to-end.
Another way to combine digital data and voice signals is to use a modem technology such as V.34 or V.92. This will also provide a digital channel for multiplexing digital data with digitized voice. The base channel can be analog. A drawback exists, however, in that the modem loses periods of audio, for example, while the modem trains and during bit errors and retrains. Moreover, the modem solution only works point-to-point and only works with compatible systems.
Yet another way is to use spread spectrum modulation of the data over the full phone line bandwidth. Energy at a frequency is spread over a wide range of frequencies for transmission, and the spread spectrum signals are collected onto their original frequency at the receiver. Spread spectrum techniques use noise-like carrier waves which are generally regarded as difficult to detect and demodulate. It is a challenge to balance restraining the audibility of the modulated data and assuring the reliability of its decoding.